ASE Practice Test (E1: Truck Equipment Installation & Repair) 3 — Questions and Answers
Question 1: What does GVWR stand for, and why is it critical when upfitting a commercial truck?
- Gross Vehicle Weight Ratio — the fuel economy rating
- Gross Vehicle Weight Rating — the maximum permissible loaded weight of the vehicle including the truck, body, equipment, cargo, and passengers (Correct answer)
- General Vehicle Work Rating — the truck's payload limit only
- Ground Vehicle Width Restriction — the width limitation for road use
Correct answer: Gross Vehicle Weight Rating — the maximum permissible loaded weight of the vehicle including the truck, body, equipment, cargo, and passengers
GVWR (Gross Vehicle Weight Rating) is the maximum safe operational weight of a fully loaded vehicle as rated by the manufacturer. When upfitting, the weight of the body, equipment, tools, and cargo plus the base vehicle weight must not exceed the GVWR. Exceeding GVWR is illegal (overweight violations), unsafe (reduced braking, structural overload), and voids warranty. Upfitters must calculate the curb weight plus the upfit weight to determine available payload capacity.
Question 2: A crane mounted on a truck body develops hydraulic drift (the crane boom slowly lowers when the control valve is in the neutral position). What component is MOST likely causing this?
- Faulty hydraulic pump worn beyond service limits
- Internal leakage past the control valve spool or cylinder piston seals (Correct answer)
- Low hydraulic fluid level in the reservoir
- Faulty PTO that is slipping under load
Correct answer: Internal leakage past the control valve spool or cylinder piston seals
Hydraulic drift occurs when pressurized fluid bypasses the load-holding mechanism and returns to the reservoir or opposite side of the cylinder. In the neutral position, the control valve should block all fluid flow. Internal leakage past a worn or contaminated control valve spool, or past the cylinder piston seal, allows the load to push the cylinder down slowly. A counterbalance valve or load check valve, if present and malfunctioning, can also cause drift.
Question 3: When installing a flat-bed body on a pickup or cab-chassis, what must be done to ensure the body is level?
- Use self-leveling bolts on all four corners
- Shim the body mounting locations to achieve a level flatbed, measuring both side-to-side and front-to-back with a precision level (Correct answer)
- Inflate the rear tires to maximum pressure to raise the rear
- Level the bed by eye only
Correct answer: Shim the body mounting locations to achieve a level flatbed, measuring both side-to-side and front-to-back with a precision level
Truck frame rails are not always perfectly level side-to-side or front-to-back due to manufacturing tolerances and frame design. Shimming body mounting blocks adjusts the height at each mounting point to achieve a level flatbed surface. A precision level placed at multiple locations on the bed confirms levelness. This is important for load containment, tail-lift operation, and professional appearance. An unlevel flatbed can cause cargo shifts during transport.
Question 4: What is the purpose of a multiplexed wiring system (CAN bus or SAE J1939) in a modern commercial upfitted truck?
- To carry high-current power directly to all accessories
- To allow multiple electronic modules and body equipment to communicate over a shared data network using low-current signal wires, reducing wiring complexity (Correct answer)
- To eliminate the need for a main battery
- To provide wireless communication between the truck and dispatch
Correct answer: To allow multiple electronic modules and body equipment to communicate over a shared data network using low-current signal wires, reducing wiring complexity
Modern commercial trucks use CAN bus (J1939 for heavy trucks) multiplexed wiring. Instead of a separate wire for every function, multiple modules share a two-wire data bus and communicate digitally. Body builders and upfitters must interface their equipment through the truck's body builder module or via approved connections to this bus. Improper CAN bus interference can disable critical vehicle systems including ABS, engine control, and instrument clusters.
Question 5: A telescoping aerial lift on a utility truck will not extend beyond a certain point and has a warning light on the control panel. What should the technician check FIRST?
- Replace the hydraulic pump immediately
- Check the load moment indicator (LMI) or overload sensor system — the lift may be preventing extension due to a sensed overload condition (Correct answer)
- Check the hydraulic fluid temperature
- Replace the boom extension cylinder seals
Correct answer: Check the load moment indicator (LMI) or overload sensor system — the lift may be preventing extension due to a sensed overload condition
Aerial lifts and cranes are equipped with load moment indicators (LMI) or overload protection systems that prevent operation beyond rated capacity. If the system senses that extending further would exceed the rated load moment (load × radius), it locks out further extension and activates a warning. The technician must verify the load, boom angle, and extension against the load chart. If not overloaded, the LMI sensor or system itself may require calibration or diagnosis.
Question 6: When installing a refrigeration unit on a cargo van or truck body, what ventilation requirement must be met for the condenser unit?
- The condenser only needs ventilation during winter operation
- The condenser must have unrestricted airflow through it — typically ducted to the exterior — to reject heat efficiently; blocked condenser airflow causes high head pressure and poor cooling performance (Correct answer)
- The condenser can be mounted inside the cargo area if properly insulated
- Ventilation is only required for the evaporator unit inside the cargo area
Correct answer: The condenser must have unrestricted airflow through it — typically ducted to the exterior — to reject heat efficiently; blocked condenser airflow causes high head pressure and poor cooling performance
Refrigeration systems work by transferring heat from inside the cargo box to the condenser, which rejects it to the ambient air. The condenser must have a supply of cool ambient air flowing through its fins and a path for the heated air to exhaust away. If condenser airflow is blocked or the unit recirculates its own discharge air, head pressure rises, the compressor is overloaded, and cooling capacity drops significantly. Proper ducting and airflow planning are critical during installation.
ASE Practice Test (E1: Truck Equipment Installation & Repair) 3
What does GVWR stand for, and why is it critical when upfitting a commercial truck?